Essentially, an air molecule doesn't have enough energy to register at your hearing sensors, that is, to move your eardrum (or cochlear hairs).

Though, now that I'm thinking about it, if the white noise generator I bought to help me sleep is really good at producing white noise with uniform power at high enough frequencies, an air molecule would have enough energy to move my eardrums. I would also be on fire.

And if my white noise generator is really really good at producing white noise with power uniform across all frequencies, the noise's mass-energy will cause my bedroom to collapse into a black hole and I will be unable to leave a 5 star review on Amazon.